1. Field of the Invention
This invention relates to a synthetic leaflet aortic or mitral heart valve prosthesis.
2. Description of the Prior Art
Prosthetic heart valves have many forms and designs and have been used for more than 20 years for treatment of heart patients when replacement of a diseased natural valve or malfunctioning prosthesis is the treatment of choice. Although prosthetic valves have been made in numerous configurations and from many different materials, none has been found to answer all of the requirements for durability, biocompatability, nonthrombogenicity and hemodynamic excellence. Basically, there are two types of heart valve prostheses: mechanical valve prostheses and natural tissue valve prostheses. Mechanical valves, although very durable and hemodynamically acceptable (in some forms), have proven to be thrombogenic. Tissue valves, on the other hand, are relatively nonthrombogenic but exhibit relatively poor hemodynamics and questionable durability.
Other heart valves have been designed using synthetic materials in configurations similar to the natural tissue valves and in other dissimilar configurations. The heart valve shown in U.S. Pat. No. 2,832,078, for example, employs sacs or membrane sections of polyfluoroethylene mounted within a stainless steel tubular frame, the sacs filling upon closure of the valve and collapsing outwardly and against the steel frame when the flow or pressure of blood is reversed. A similarly functioning valve design, employing terylene-silicone rubber synthetic materials, is shown in U.S. Pat. No. 3,736,598. Heart valves of these configurations require an outer ring structure against which the sac-like membranes collapse upon opening of the valve.
Further membrane valves structures for temporary use are shown in the U.S. Pat. Nos. 3,671,979 and 4,056,854. The design of the first cited patent employs an umbrella shaped membrane wherein in the apex of the umbrella resides in the vessel in the direction in which the flow of blood is to be prevented, and the apex is affixed at or near the distal end of a flexible catheter so that the catheter and umbrella membrane may be placed in a blood vessel in proximity to the natural valve. In operation, the membrane of the valve callapses and folds against the catheter to permit the flow of blood in the proper direction between the centrally disposed catheter and the vessel wall, and when flow in that direction ceases and flow starts in the reverse direction, the force of the blood flow is supposed to cause the membrane to open so that the free edge of the valve membrane contacts the inner wall of the vessel to occlude the vessel to further reversed flow of blood.
The artificial heart valve design of the U.S. Pat. No. 4,056,854 is again a valve supported at the end of a catheter and consists of a tubular, sac-like membrane attached at one end to a ring metallic support of a springing material which is supported by the catheter in contact with the blood vessel wall. Fow of the blood in the proper direction causes the membrane to open against the downstream surface of the blood vessel wall, and reverse blood pressure causes the free end of the membrane to collapse inward against itself and against the catheter to stop blood flow.
These catheter mounted valve designs are not suited for permanent implantation in a tissue annulus for permanent replacement of the diseased or defective heart valve and can only be used temporarily in blood vessels. Mitral placement of these valves would not be possible and aortic placement would not be efficient. A further problem arises from the use of a catheter support which provides areas of downstream blood stagnation which could increase the incidence of thrombus formation leading to reduction of a valving action and possible fatal thromboembolic complications.
A further heart valve design is depicted in U.S. Pat. No. 3,898,701 which also employs an open sac-like silicone rubber or plastic membrane with one end supported by a ring sutured to the valve annulus. A central disposed separator is necessary to prevent inversion of the free end of the membrane. This design suffers from the necessity of an outer ring and separator which can lead to thrombus formation.
The various designs of heart valve prostheses employing synthetic materials all suffer to one degree or another, either from the material employed or the design configuration, from the incidence of thrombus formation. Furthermore, the designs that have found widespread medical acceptance also employ rigid or semi-rigid valve ring structures which do not enjoy the ability to flex or move with the movement of the tissue annulus as the heart expands and contracts, reducing myocardial efficiency and leading to perivalvular leaks and valvular dehiscence in a significant number of patients. In addition, the ring structures occupy up to 50 percent of the available annular area for blood flow, thus reducing cardiac efficiency and raising transvalvular pressure gradients.